Thermal Expansion Of Moist Wood

Linear thermal expansion of wood, as measured with sealed cylindrical specimens at constant moisture content, generally increased with the amount of bound water. This could be expected on the basis of the low stiffness of moist wood. Near the fiber saturation point and above, shrinkage from internal drying was superimposed on true thermal expansion. At temperatures above 0 C during heating, water migrated out of fiber-saturated cell walls; the resulting shrinkage reduced the expansion significantly and between 20 and 70 C even led to contraction. At freezing temperatures during cooling, moisture diffused out of the saturated cell walls and condensed as ice crystals in the cell cavities; the resulting shrinkage supplemented true thermal contraction and caused large coefficients of thermal expansion in a broad sense.Thermal expansion was largest tangentially and smallest in the longitudinal direction. Tangential coefficients of thermal expansion at 12% moisture content and room temperature averaged 53 X 10-1 mm/(mm C) for redwood, 70 X 10-6 mm/(mm C) for northern red oak, 38 X 10-6 mm/(mm C) for Douglas-fir and yellow birch. Coefficients in the longitudinal direction and for plywood were below 10 X 10-6 mm/(mm C) on the average

Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics

A simple but general microscopic mechanism to understand the interplay between the electric and magnetic degrees of freedom is developed. Within this mechanism, the magnetic structure generates an electric current which induce an counterbalance electric current from the spin orbital coupling. When the magnetic structure is described by a single order parameter, the electric polarization is determined by the single spin orbital coupling parameter, and the material is predicted to be a half insulator. This mechanism provides a simple estimation of the value of ferroelectricity and sets a physical limitation as well.Comment: 4 pages, 1 figur

Ant Clustering with Locally Weighting Ant Perception and Diversified Memory

Ant clustering algorithms are a robust and flexible tool for clustering data that have produced some promising results. This paper introduces two improvements that can be incorporated into any ant clustering algorithm: kernel function similarity weights and a similarity memory model replacement scheme. A kernel function weights objects within an ant’s neighborhood according to the object distance and provides an alternate interpretation of the similarity of objects in an ant’s neighborhood. Ants can hill-climb the kernel gradients as they look for a suitable place to drop a carried object. The similarity memory model equips ants with a small memory consisting of a sampling of the current clustering space. We test several kernel functions and memory replacement schemes on the Iris, Wisconsin Breast Cancer, and Lincoln Lab network intrusion datasets. Compared to a basic ant clustering algorithm, we show that kernel functions and the similarity memory model increase clustering speed and cluster quality, especially for datasets with an unbalanced class distribution, such as network intrusion

Asset Trading Volume with Dynamically Complete Markets and Heterogeneous Agents

The trading volume of long-lived securities with recursive payoffs, such as equity, is generically zero in infinite-horizon recursive pure exchange Lucas asset models with heterogeneous agents. In equilibrium, there is no portfolio rebalancing of such assets. More generally, the end-of-period portfolio of long- and short-lived securities is constant over time and states in the generic economy. We also present a nonrobust formulation of dynamically complete markets which does have nonzero trading volume in equilibrium. The comparisons show that any theory of asset trading volume will be very sensitive to small changes in model specifications.

The effects of exercise during pregnancy on placental composition : A systematic review and meta-analysis

Introduction Morphological changes to the placenta occur as the demands of the foetus increase throughout gestation. Physical activity during pregnancy is known to benefit both the mother and infant, however the impact of antenatal exercise training on placental development is less known. The aim of this systematic review and meta-analysis was to investigate the effects of exercise training during pregnancy on measures of placental composition. Methods Six electronic databases were searched from inception to June 2021 for studies comparing regular antenatal exercise with either usual maternal care or no exercise for its effect on measures of placental morphological composition. Meta-analyses were performed for placental weight and the placental weight to birthweight (PWBW) ratio. Results Seven randomised controlled trials and two cohort studies were included in the systematic review and meta-analysis (n = 9). There was no significant difference in placental weight (mean difference (MD) = -9.07g, p = 0.42) or the PWBW ratio (MD = 0.00, p = 0.32) between exercise and control groups. Parenchymal tissue volume was higher, represented by an increase in villous tissue, and non-parenchymal volume was lower in women who exercised regularly compared to those that were not exercising during pregnancy. Discussion Exercise training during pregnancy may not alter placental weight or the PWBW ratio. However, findings from this review indicate that antenatal exercise training can promote advantageous morphological changes to placental tissues

Magnetization Dissipation in Ferromagnets from Scattering Theory

The magnetization dynamics of ferromagnets are often formulated in terms of the Landau-Lifshitz-Gilbert (LLG) equation. The reactive part of this equation describes the response of the magnetization in terms of effective fields, whereas the dissipative part is parameterized by the Gilbert damping tensor. We formulate a scattering theory for the magnetization dynamics and map this description on the linearized LLG equation by attaching electric contacts to the ferromagnet. The reactive part can then be expressed in terms of the static scattering matrix. The dissipative contribution to the low-frequency magnetization dynamics can be described as an adiabatic energy pumping process to the electronic subsystem by the time-dependent magnetization. The Gilbert damping tensor depends on the time derivative of the scattering matrix as a function of the magnetization direction. By the fluctuation-dissipation theorem, the fluctuations of the effective fields can also be formulated in terms of the quasistatic scattering matrix. The theory is formulated for general magnetization textures and worked out for monodomain precessions and domain wall motions. We prove that the Gilbert damping from scattering theory is identical to the result obtained by the Kubo formalism.Comment: 15 pages, 1 figur

Calculations of giant magnetoresistance in Fe/Cr trilayers using layer potentials determined from {\it ab-initio} methods

The ab initio full-potential linearized augmented plane-wave method explicitly designed for the slab geometry was employed to elucidate the physical origin of the layer potentials for the trilayers nFe/3Cr/nFe(001), where n is the number of Fe monolayers. The thickness of the transition-metal ferromagnet has been ranged from $n=1$ up to n=8 while the spacer thickness was fixed to 3 monolayers. The calculated potentials were inserted in the Fuchs-Sondheimer formalism in order to calculate the giant magnetoresistance (GMR) ratio. The predicted GMR ratio was compared with the experiment and the oscillatory behavior of the GMR as a function of the ferromagnetic layer thickness was discussed in the context of the layer potentials. The reported results confirm that the interface monolayers play a dominant role in the intrinsic GMR.Comment: 17 pages, 7 figures, 3 tables. accepted in J. Phys.: Cond. Matte

In-situ surface technique analyses and ex-situ characterization of Si1-xGex epilayers grown on Si(001)-2 ×1 by molecular beam epitaxy

Si1-xGex epilayers grown by Molecular Beam Epitaxy on Si(001) at 400 ○C have been analyzed in-situ by surface techniques such as X-ray and Ultraviolet Photoelectron Spectroscopies (XPS and UPS), Low Energy Electron Diffraction (LEED) and photoelectron diffraction (XPD). The Ge surface concentrations (x) obtained from the ratios of Ge and Si core level intensities are systematically higher than those obtained by the respective evaporation fluxes. This indicates a Ge enrichment in the first overlayers confirmed by Ge-like UPS valence band spectra. The structured crystallographic character of the epilayers is ascertained by LEED and XPD polar scans in the (100) plane since the Ge Auger LMM and the Si 2p XPD intensity patterns from the Si1-xGex epilayers are identical to those of the Si substrate. The residual stress in the epilayer is determined by ex-situ X-ray diffraction (XRD) which also allows, as Rutherford Back Scattering (RBS), Ge concentration determinations

Bond Portfolios and Two-Fund Separation in the Lucas Asset-Pricing Model

The two-fund separation theorem from static porfolio analysis generalizes to dynamic Lucas-style asset model only when a consol is presemt. If all bonds have finite maturity and do not span the consol, then equilibrium will devitate, often significantly, from two-fund separation even with the classical preference assumptions. Furthermore, equilibrium bond trading volume is unrealistically large, particularly for long-term bond, and would be very costly in the presence of transaction costs. We demonstrate that investors choosing two-fund portfolios with bond ladders that approximately replicate consols do almost as well as traders with equilibrium investment strategies. This result is enhanced by adding bonds to the collection of assets even if they are not necessary for spanning. In the light of these results, we argue that transaction cost considerations make portfolios using two-fund separation and bond laddering nearly optimal investment strategies.Dynamically complete markets, general equilibrium, consol, bonds, interest rate fluctuation, reinvestment risk, bond laddering

Full-Field Measurement of Residual Stresses in Composite Materials Using the Incremental Slitting and Digital Image Correlation Techniques

Background The slitting method is a widely used destructive technique for the determination of residual stresses. Because of the rich data content of the full-field methods, optical techniques such as digital image correlation (DIC) are replacing strain gages for surface measurements. Objective The objective of the current paper is to overcome the difficulties that arise in using the DIC technique combined with the slittingmethod. The present noise, low signal-to-noise ratio, and systematic errors are themain impediments to the use of DIC in the slitting method. Methods An approach based on the eigenstrain concept was exploited to ascertain the optimum region of interest (ROI) for the analysis. After that, a robust procedure was implemented to utilize the DIC method while excluding the rigid body motion and rotation artifacts from the obtained displacements. Results Different slitting steps may cause dissimilar rigid bodymotions and rotations of the specimen. The proposedmethod was able to eliminate all of these different shears and stretches in the images simultaneously. The slitting experiment was conducted on a symmetric cross-ply composite specimen, and the slit progressed down to half the thickness. Although some rigid body motions were large, the method managed to exclude all of them for eight slitting steps. Conclusion A comparison made between the results of the current method and those of the strain gage technique shows that they are in acceptable agreement with each other, and this full-field method can be extended to smaller scales or other destructive techniques